The purpose of this study is to provide insights on the function of noble metals, namely Pt-Pd catalytic system, on the hydrodesulfurization (HDS) of alkyl-substituted dibenzothiophenes (a-DBTs) by means of kinetic modeling and contribution analyses. A series of Pt-Pd systems (1% wt. nominal loading) supported on gamma-Al2O3 (0-100, 20-80, 50-50, 80-20 and 100-0; %mol Pt-%mol Pd) are synthesized and evaluated during the HDS of 4,6dimethyldibenzothiophene (4,6-DMDBT) at operating conditions relevant for industry: 320 degrees C, 500 ppm of S and an H-2 pressure of 5.5 MPa. A summary of their characterization is presented as reference herein. Kinetic model based on a Langmuir-Hinshelwood-Hougen-Watson (LHHW) mechanism and contribution analysis based on predicted reaction rates give rise to the following findings: the bimetallic catalyst 8Pt-2Pd/gamma-Al2O3 (80-20; %mol Pt-%mol Pd) leads to the highest activity; in all Pt-Pd/gamma-Al2O3 systems, Pt favors desulfurization reactions, i.e., 4,6-DMDBT to 3,3'-dimethylphenyl (3,3'-DMBP) and 4,6-dimethyltetrahydrodibenzothiophene (4,6-DM-th-DBT) to MCHT, whereas Pd favors hydrogenation of 4,6-DMDBT to 4,6-DM-th-DBT; and 4,6-DMDBT and methylcyclohexyltoluene (MCHT) are the hydrocarbons with the lowest and highest affinity to be adsorbed on the active sites from the studied Pt-Pd/gamma-Al2O3 systems, respectively. (C) 2014 Elsevier B.V. All rights reserved.